Optical digitization of a three dimensional (3-D) contour using a camera, structured light, and triangulation is known. Optical digitization includes using a structured light or radiation source such as, for example, a laser line projected at a known incident angle onto an object to be measured. The camera is located with the laser line in the camera's view.
Digitization systems of this type are typically calibrated to relate observed line location with contour data. The calibration can be performed by placing an object in the field of view in front of the laser line and camera and moving either the object or the camera/laser line assembly. A series of images are recorded with the relationship between the camera/laser line and the object changing a known amount between the recording of each image. The recorded image data is compared with the known geometry of the object in the field of view to determine and assign geometry values to the laser line's observed location in the camera's image data. In this fashion, the system learns how to derive geometric data from the laser line's location in the camera image. That is, the digitization system is calibrated.
There are a number of variations of the above-discussed concept. For example, one variation uses a light source of a different structure such as a matrix of lines, a grid pattern, dots, etc. The digitization system may use a polar axis rather than a linear axis for the transport of the object being measured through the field of view of the camera and the structured light source.
Systems using the basic optical digitization discussed above are known. However, heretofore such systems have been large and expensive to build. This and other disadvantages limit the application of the laser scanning technology to applications where expense and size are not relatively important factors such as applications like high end medical applications and service bureaus. For example, a 3-D digitization system using aspects of the basic scanning technique discussed above, i.e., a light source and a camera sensor, is disclosed in U.S. Pat. No. 4,705,401 to Addleman et al.
Other technologies may be used to measure the geometry of the undersurface of the object to be measured, such as a foot. These technologies include (1) contact digitizing wherein gauge pins spaced at known intervals are urged upward beneath the foot and sample the contour periodically, and (2) optical triangulation where radiation of a known characteristic is projected against the subject foot such that the resulting shape of the radiation as it contacts the foot is observed by a sensor, typically a camera. A processor is used to evaluate the observed image to determine the contour data of the object (e.g., the foot) being measured.
Contact digitizing is generally the preferred method of obtaining the underside of a foot when the merits of the resulting data are the exclusive criterion. A contact digitizer supports the foot while measuring. Supporting the foot allows a full weight bearing measurement to be made, while not allowing the foot to completely collapse against the flat, top surface of the scanner. This yields a supportive data set that captures the extension of the foot when weight is applied.
A laser scanner has a clear plate between the scanning mechanism and the subject being measure. In the instance of measuring a foot, if the foot is suspended above the glass plate (i.e., left free the air) the data produced by the scanner matches the shape of the foot. However, this technique requires that the foot be measured in an unweighted position. The contour date obtained from the foot in the unweighted position is not very desirable since the foot can expand by as much as size and one-half when weight is applied thereto in the course of walking. The contour produced by an unweighted measurement will over Support the foot and cause discomfort. Yet, if the foot is placed against the clear plate to simulate the weight bearing of the foot, the bottom of the subject foot is completely flat. This produces an uncomfortable and unnatural, distorted shape.
Laser scanners also have a number of other problems associated with placing the foot against the clear plate such as (1) fogging where, if the foot is not completely dry, a fog is produced on the glass that tends to compromise the measurement accuracy of the foot since the shape of the subject foot is at least partially obscured by the fog; and (2) surface refraction caused by a lack of contrast of the subject foot due to, for example a light skin tone of a bare foot placed against the clear glass plate that disperses the projected radiation when it contacts the foot. The projected light disperses inside the body. It then refracts back through the clear plate. This produces an ambiguous radiation observation, as the radiation is diffused.